Q4 - aleontologists had long supposed that the dinosaur Dip

[mshinners]

Question Type:
Necessary Assumption

Stimulus Breakdown:
DINOS! (Yes, I'm going to do this every time.)

An old theory about the Diplodocus's eating habits (eating from tall trees) has recently been disproven. The models that disproved the old theory showed that the dino could have eaten vegetation on the ground or underwater. The author then says this theory "must" be true."

Answer Anticipation:
Extreme language in the conclusion is generally a good place to start looking for a flaw, and we have an extreme word here: "must". While the evidence certainly provides information that the Diplodocus might have had this diet, it's a large jump to a conclusion that this "must" be their diet.

When an Necessary Assumption question chooses a single explanation as correct, alternative explanations are generally ruled out by the correct answer. I'd be on the lookout for anything that rules out other possible eating habits.

Correct answer:
(D)

Answer choice analysis:
(A) Unnecessary comparison. While similar physiology leading to similar behavior might strengthen the argument (might), it certainly isn't necessary to it. Diplodocuses (Diplodoci?) could have engaged in behavior that similar, modern animals don't.

(B) Since vision isn't necessary to finding food/eating, this answer is also not necessary.

(C) Degree/out of scope. This answer is very extreme with "impossible". While the argument does rely on the Diplodocus not eating from the tops of trees, it doesn't have to be impossible to supply blood to the brain for that to happen. It could just result in severely decreased blood supply, which would be enough to potentially prevent eating from the tops of trees.

(D) Bingo. We needed an answer that rules out possible food sources other than ground/underwater ones. While we learned the Diplodocus couldn't reach up with its neck, it was possible it had other ways to reach the tops of trees. This answer states that it didn't, in fact, have other methods, ruling out treetops as a potential source for food. If we negate this answer - Diplodocus had other ways (than lifting its head) of accessing high-growing vegetation - that kills our argument.

(E) Opposite. The argument relies on the Diplodocus not having other methods of eating from treetops, not from underwater. It's possible to talk yourself into this answer by thinking that, since the argument relies on accessing these plants with its neck, other methods of reaching this food were relevant to the argument. However, negating it - Diplodocus was able to browse for underwater vegetation through these other means - if anything makes it more likely that this was the diet they used. If the negation helps the conclusion, it's time to move on!

Takeaway/Pattern:
Extreme language in the conclusion is generally related to the flaw. Additionally, Necessary Assumption questions generally have weaker answers (because a strong answer might be too strong to be necessary). However, when the conclusion is strong, you can have a stronger answer. The LSAT has been increasing the frequency of these strong conclusion/strong answer pairs on Necessary Assumption questions.

#officialexplanation

[seychelles1718]

I am having a hard time understanding this argument...

How do you know if the author is excluding the possibility of Diplos eating high growing vegetation via other ways based on the author's conclusion?

The author merely concluded "diplo must have fed on plants on or near the ground or underwater." How does such statement preclude diplo eating high growing vegetation? The author only mentioned diplo cannot eat high growing vegetation through NECK MOVEMENT. He didnt totally reject that diplo can eat high growing plants via other ways.

If a qualifier such as "only" were inserted at the end of the conclusion, I think D can definitely be the assumption of the argument. But isn't the possibility of Diplo eating high growing vegetation via other means completely compatible with the author's conclusion?

[ohthatpatrick]

I agree, I don't like it too much.

As an isolated claim, "D must have fed on plants on or near the ground, or underwater" doesn't seem to preclude feeding on plants elsewhere. It sounds like we're only promising that "AT LEAST one of these options was the case".

In context, though, I see where LSAT felt like this conversation was presenting "on ground, near ground, underwater" as an exhaustive list of D's food sources.

The lead up of, "We had long supposed that D ate high leaves by raising its neck",
followed by, "but the neck couldn't have been raised"
followed by, "thus, D must have (just) fed on plants on or near the ground, or underwater."

I inserted the "just", or the "only", that we crave. But we're supposed to hear the author's final conclusion move as fatalistic resignation that "clearly, high leaves weren't possible, so it must have fed on low stuff"

The fact that we're listing X or Y or Z also helps to convey that we're providing the exhaustive list of food source possibilities.